PETpla.net Insider 09 / 2015

MATERIAL / RECYCLING 10 PET planet insider Vol. 16 No. 09/15 www.petpla.net Rethinking the next generation of PET recycling Introducing new technology in the field of plas- tics recycling has always been the aim of Next Generation Recyclingmaschinen GmbH from Austria. The LSP process (Liquid State Poly- condensation) for PET recycling combines increased of Intrinsic Viscosity (IV) and excel- lent decontamination properties with low energy consumption. The global annual PET consump- tion reaches some 20 million tons and the PET fiber business is approxi- mately twice as big. Reasons enough to rethink the general approach of recycling the material and to start taking full advantage of PET’s proper- ties by designing a new process. Improving PET properties in the liquid state PET, like all polymers, consists of polymer chains. The chains length determines the material strength and its viscosity (measured as IV). Each step in processing the material (fiber spinning, film extrusion, injection moulding, etc.), leads to “breaking” some of the chains apart, thereby reducing material strength and low- ering the viscosity of the material towards easier flowing. The shotened polymer chains can be restored in length by polycon- densation. The traditional method of achieving this is Solid State Polycon- densation (SSP). Crystalline pellets or PET bottle flakes are heated to about 200 to 240°C and kept at this temperature for several hours, result- ing in an increase of IV by approx. 0.01 to 0.02dl/g per hour resp. 0.05 to 0.06dl/g in the case of flakes. Liquid State Polycondensation (LSP), on the other hand, takes advantage of the material being at a higher temperature range (270 to 280°C) and therefore sports an increased reaction-speed of the polycondensation. The LSP process can increase the IV by 0.01 to 0.02 dl/g within minutes and keeps the desired IV within a narrow range of 0.015 dl/g. FDA non-objection-letter for 100% food application issued The backbone of the LSP pro- cess is P:REACT. In this reactor the surface/volume-ratio of molten PET is increased by forming strands and high performance vacuum is applied. This configuration enables easy decontamination of the material from harmful chemicals and makes the LSP process suitable for food-con- tact. A “challenge-test” conducted by Fraunhofer IVV / Germany provides the required scientific evidence for the decontamination performance of the process. In this test PET bottle flakes are purposely contaminated with vari- ous different chemicals. These flakes are then recycled by the LSP-Process and the remainders of the chemicals are analysed by Fraunhofer. The graph shows the cleaning capac- ity of the LSP process, being close to 100%. The yellow curve indicates the requirements by EFSA (European Food Safety Authority). Based on these tests FDA has issued a non- objection-letter for applications in 100% food-contact in November 2013. P:REACT demonstrates outstanding performance The first P:REACT unit was installed in March 2015 and is pro- ducing rPellets from fibre scrap. The PET-fibres are collected from various points in the spinning process and contain up to 15% of spin oil. A shredder-feeder-extruder combina- tion provides the PET melt and a first degassing. As the melt is introduced into P:REACT the IV is lifted from 0.56 dl/g to 0.66 dl/g within a variation of less than +/- 0.015 dl/g. The required elimination of the spin oil content comes automatically with the high decontamination performance of the unit. The equipment owner reuses the rPellets from P:REACT in his spin pro- cess simultaneously with virgin PET without any spin process adaption. Figure 1: PET process-comparison (data/graphic: NGR) SSP (Solid State Polycondensation) LSP (Liquid State Polycondensation) State of PET Solid / crystalline Liquid (melt) Environment Inert gas or vacuum Vacuum Typical Temperature (200-240) °C (270-280) °C IV – Lift-Speed (0.01 – 0.02) dl/g (rPellet) (0.05 – 0.06) dl/g (flake) per hour (0.01) dl/g per minute Figure 2: Decontamination performance of the LSP-process (data: Fraunhofer IVV, graphic: NGR) Recycling S p e c i a l